Piezoelectric motor and method for actuating same

ABSTRACT

The piezoelectric motor ( 6 ) comprises a stator ( 1 ) and a runner ( 4 ) which form a gap ( 7 ) as well as comprising a piezoelectric transducer ( 3 ) which is connected to the stator ( 1 ) or the runner ( 4 ) and which with the stator ( 1 ) or the runner ( 4 ) forms a resonator ( 1,3;4,3 ), wherein the resonator ( 1,3; 4,3 ) may be excited in a main oscillation direction (H), characterised in that the stator ( 1 ) comprises an engagement surface ( 1   a ) facing the runner ( 4 ), or the runner ( 4 ) an engagement surface which faces the stator ( 1 ), and that the stator ( 1 ) or the runner ( 4 ) comprises an elastic advance element ( 5 ) which bridges the gap ( 7 ) between the stator ( 1 ) and the runner ( 4 ) in a manner such that the advance element ( 5 ) at least temporarily lies on the engagement surface ( 1   a ). The advance element ( 5 ) comprises a first part-section ( 5   c ) as well as a second part-section ( 5   d ), wherein the part-sections ( 5   c,    5   d ) have a different resonant frequency.

The invention relates to a piezoelectric motor according to the preambleof claim 1. The invention relates further to a method for driving apiezoelectric motor according to the preamble of claim 20.

A piezoelectric motor is known from the document EP 1 098 429 A2 whichcomprises at least two piezoelectric longitudinal actuators which aredisplaced by 90 degrees to one another and which act on a shaft via anannularly designed coupling element and by way of this set the shaftinto rotation. For activating the individual longitudinal actuators, onerequires sinusoidal voltage signals which need to have a constant phaserelation of 90 degrees.

This piezoelectric motor has the disadvantages that several oscillationbodies are present which are to be matched to one another, that onlysmall torques may be produced, that a large wear occurs between thecoupling element and the shaft, and that the piezoelectric motor isrelatively expensive.

It is the object of the present invention to provide a more advantageouspiezoelectric motor. This object is achieved with a piezoelectric motorhaving the features of claim 1. The dependent claims 2 to 19 concernfurther advantageous formations. The object is achieved further with amethod for driving a piezoelectric motor having the features of claim20. The dependent claim 21 concerns a further advantageous formation ofthe method.

The object in particular is achieved by a piezoelectric motor comprisinga stator and a runner which form a gap, wherein the stator or the runneris connected to a piezoelectric transducer which together with thestator or runner forms a resonator, wherein the resonator may be excitedin a main oscillation direction, and wherein the stator comprises anengagement surface facing the runner or the runner an engagement surfacefacing the stator, and the stator or the runner comprises an elastic(flexible) advance element which runs at an angle to the mainoscillation direction and which bridges the gap between the stator andthe runner in a manner such that the advance element at leasttemporarily lies on the engagement surface. The resonator sets theadvance element into an oscillating micro-movement so that the advanceelement periodically exerts an advance force onto the engagementsurface, and the runner experiences an advance movement with respect tothe stator, so that the runner is moved.

In a particularly advantageous formation, the piezoelectric motor isdesigned as a rotation motor, with a circular runner designed as arotor, and a circular annular stator enclosing the rotor. The stator isequipped with one or two piezoelectric, annular transducers whichtogether with the stator form a resonator. This resonator has a mainoscillation direction running radially to the centre of rotation of therotor, so that the resonator executes a micro-movement running in theradial direction. The advance element is connected to the stator or therotor, is preferably designed running in an essentially straight line,and runs preferably at an angle larger than 0 degrees with respect tothe main oscillation movement, in particular at an angle between 20 and60 degrees. In one advantageous design a plurality to multitude ofadvance elements are arranged mutually uniformly distanced in thecircumferential direction of the stator or of the rotor, wherein alladvance elements lie on the same engagement surface. There results apiezoelectric motor which rotates clockwise or anticlockwise dependingon the alignment of the advance element.

In a further advantageous design the advance element is not designedrunning in a straight line, but comprises a first part-section as wellas a second part-section which meet at a sharp bend location. The firstas well as the second part-section have a different resonant frequency(natural frequency) which has the result that the piezoelectric rotationmotor executes a clockwise rotation or anticlockwise rotation dependingon the frequency of the resonator. The two part-sections may oscillatefreely on operation of the motor. The first part-section at the sametime oscillates with respect to the stator or rotor connected to it, thesecond part-section oscillates with respect to the first part-sectionand acts on the engagement surface.

In a further, advantageous design the piezoelectric motor according tothe invention is designed as a linear motor, wherein the stator extendsin the linear direction, and the runner is movably mounted in thisdirection.

The piezoelectric motor according to the invention has the followingadvantages:

-   -   that it may be designed to rotate anticlockwise, clockwise or in        both directions,    -   that the maximum torque and the speed may be set via the        engagement angle of the advance element with respect to the        engagement surface,    -   that the engagement surface is relatively large so that the        advance element acting on the engagement surface has only a low        wear as a result of this,    -   that the advance element acts on the engagement surface without        a hammering movement, which has the result of a low wear,    -   that only a single resonator is required for operation, which in        contrast to the known use of several resonators considerably        simplifies the tuning of the mechanical resonance circuit,    -   that the construction is very simple,    -   that the manufacturing costs are relatively low,    -   that it is very small and quiet, furthermore may be operated        largely without any slip and has a fine resolution with respect        to the rotation angle,    -   that the shaft may be driven without any bending moment,    -   that it may be operated at a low rotational speed, has a high        torque and thus may be operated without transmission gears,    -   that it has a short run-up time and stop time in the range of        milliseconds,    -   that it has a low constructional volume,    -   that it emits almost no electromagnetic scatter field,    -   and that it has a high efficiency.

Several embodiment examples of the device according to the invention arehereinafter described in detail by way of the following figures. Thereare shown in:

FIG. 1 a a lateral view of a radially oscillating stator as well as itscontracted state;

FIG. 1 b a lateral view of a radially oscillating stator as well as itsexpanded state;

FIG. 1 c a section through the stator along the section line A-A;

FIG. 2 a a lateral view of a further radially oscillating stator as wellas its expanded state;

FIG. 2 b a lateral view of a further radially oscillating stator as wellas its contracted state;

FIG. 2 c a section through the stator along the section line B-B;

FIG. 3 a a lateral view of a rotor running in the anticlockwisedirection;

FIG. 3 b a schematic lateral view of a rotor running in theanticlockwise direction;

FIG. 4 a lateral view of a rotor running in the clockwise direction;

FIG. 5 a a lateral view of a rotor running in the anticlockwisedirection, which is capable of running in both rotation directions,

FIG. 5 b a lateral view of a rotor running in the clockwise direction,which is capable of running in both rotational directions,

FIG. 5 c a schematic view of the rotor with the advance element;

FIG. 5 d a detailed view of a further advance element;

FIG. 6 a lateral view of a rotor which is capable of running in bothrotation directions;

FIG. 7 the frequency behaviour of the stator and its resonance curve;

FIG. 8 the first and second resonance curve of the stator;

FIG. 9 a a lateral view of a piezoelectric motor designed as an innerrunner, without any mounting;

FIG. 9 b a section through the motor represented in FIG. 9 a, along thesection line C-C;

FIG. 10 a a lateral view of a further piezoelectric motor designed as aninner runner, with a mounting;

FIG. 10 b a section through the motor represented in FIG. 10 a, alongthe section line D-D;

FIG. 11 a a lateral view of a further piezoelectric motor designed as aninner runner, without any mounting;

FIG. 11 b a section through the motor represented in FIG. 11 a, alongthe section line E-E;

FIG. 12 a a lateral view of a piezoelectric motor designed as an outerrunner, without a mounting;

FIG. 12 b a section through the motor represented in FIG. 12 a, alongthe section line F-F;

FIG. 13 a a lateral view of a piezoelectric motor designed as an outerrunner, with a mounting;

FIG. 13 b a section through the motor represented in FIG. 13 a, alongthe section line G-G;

FIG. 14 a a lateral view of a piezoelectric motor designed as an innerrunner, with a hollow runner;

FIG. 14 b a section through the motor represented in FIG. 14 a along thesection line H-H;

FIG. 15 a a lateral view of a linear motor for the anticlockwise andclockwise running;

FIG. 15 b a section through the linear motor represented in FIG. 15 aalong the section line I-I;

FIGS. 16 a, 16 b, 16 c a somewhat modified embodiment form of the motor;

FIG. 17 a a lateral view of a further linear motor for anticlockwise andclockwise running; and

FIGS. 17 a, 17 b, 17 c in each case, various variants of a linear motorwith a lateral view according to FIG. 17 a, as a section along thesection line J-J.

If hereinafter one speaks of a stator and runner or rotor, then theseterms may be exchanged with one another, since the stationary part ofthe motor indicated as the stator may also be the runner or the rotatingpart of the motor if the part indicated as the runner or rotor isarranged in a stationary manner.

FIGS. 1 a and 1 b show a resonator 1,3 consisting of a circular annularstator of metal or ceramics as well as of two annular piezoelectrictransducers 3 a, 3 b which are arranged on the stator 1 on both sidesand are firmly connected to this. The resonator 1,3 is designed in anaxially symmetrical manner with respect to the centre 4 a and in theexcited condition has a main oscillation direction H or micro-movementrunning in the radial direction with respect to the centre 4 a. At thesame time the resonator 1,3 is designed in a manner such that this inits entirety contracts, as this is indicted in FIG. 1 a by the outlineshown dashed, or that this in its entirety expands, as this is indicatedin FIG. 1 b by the outline shown dashed.

FIG. 1 c shows a section through the resonator 1,3 along the sectionline A-A.

FIG. 2 a and FIG. 2 b show a further resonator 1,3 which in contrast tothe embodiment shown in the FIGS. 1 a, 1 b may be excited in a mainoscillation direction H running radially with respect to the centre 4 a,in a manner such that the annulus width of the resonator 1,3 increasesas this is indicated in FIG. 2 a by the outline shown dashed, or thatthe annulus width of the resonator 1,3 is reduced as this is indicatedin FIG. 2 b by the outline shown dashed.

FIG. 2 c shows a section through the resonator 1,3 along the sectionline B-B.

FIG. 3 a shows a detail of a piezoelectric motor 6 which comprises aresonator 1,3 as this is disclosed in the FIGS. 1 a, 1 b, 2 a, and 2 b.The resonator 1,3 comprises an inwardly directed engagement surface 1 a.The resonator 1,3 may be excited in the main oscillation direction H sothat the engagement surface 1 a oscillates in this direction. Theengagement surface 1 b represented dashed shows the position of theengagement surface 1 a at the point in time of the maximum contractionof the resonator 1,3. A circular rotor 4 with a rotation centre 4 a isarranged within the stator 1 whilst forming a gap 7. An elastic advanceelement 5 is arranged on the surface of the rotor at an angle a to themain oscillation direction H. In an initial position the engagementsurface has the position indicated at 1 a, and the advance element 5 theposition indicated at 5 a. The advance element 5 bends during themovement of the engagement surface 1 a to the position indicated at 1 band moves into the thrust position indicated at 5 b. Since the frictionforce between the engagement surface 1 a and the advance element 5 issufficiently large, the advance element 5 remains supported on the sameposition of the engagement surface 1 a, 1 b during the contraction ofthe engagement surface from the position 1 a to the position 1 b whichis why the advance element 5 effects a force on the rotor 4 directed tothe left so that the rotor 4 undergoes an anticlockwise rotation in thedirection D. With the forward swing movement of the engagement surfacefrom the position 1 b to the position 1 a the resonator 1,3 undergoes ahigh acceleration. The friction force of the advance element 5 on theengagement surface 1 a, 1 b is very small on account of this so thatduring the forward swing movement no or only a small force acting in therotation direction D is exerted on the rotor 4 so that this undergoesessentially no movement. By way of the subsequent contraction of theresonator 1,3, the rotor 4 is however rotated again in the direction Dvia the advance element 5. As long as the resonator 1,3 oscillates inthe main oscillation direction, the rotor 4 thus executes ananticlockwise rotation in the direction D. The rotor 4 no longerexecutes a rotational direction as soon as the resonator 1,3 comes torest. The piezoelectric motor 6 may thus be started and stopped again inan infinite manner.

FIG. 3 b in detail once again shows the manner of functioning of thepiezoelectric motor 6 represented in FIG. 3 a. The resonator 1,3 withthe engagement surface 1 a is contracted in the radial direction aboutthe distance Δrs so that the engagement surface assumes the positionindicated at 1 b. At the same time the advance element is moved from theinitial position 5 a into the thrust position 5 b, and the tip 5 f ofthe advance element 5 is displaced in the rotational direction by theamount ΔUR so that the tip 5 f lying on the rotor 4 rotates the rotor 4by this amount.

FIG. 4 shows a modified embodiment of the piezoelectric motor 6 shown inFIG. 3 a in which the advance element 5, in comparison to the embodimentaccording to FIG. 3 a, is arranged running in the opposite directionwith respect to the main oscillation direction H. This has the resultthat the rotor 4 undergoes a rotation in the direction D during theoscillation of the resonator 1,3 and thus executes a clockwise rotation.With the exception of the arrangement of the advance element 5, thepiezoelectric motors 6 represented in FIG. 3 a and FIG. 4 are designedidentically.

FIGS. 5 a and 5 b show a piezoelectric motor 6 which in contrast to theembodiment represented in FIG. 4 comprises an advance element runningwith a sharp bend. The advance element 5 comprises a first part-section5 c connected to the rotor 4, as well as a part-section 5 d whichconnects thereto and which runs in the opposite direction with respectto the main oscillation direction H.

FIG. 5 c in a schematic and detailed manner shows the advance element 5represented in the FIGS. 5 a and 5 b.

FIG. 5 d shows an embodiment of an advance element 5 running with asharp bend with a first part-section 5 c, a narrowing location 5 e whichruns into the second part-section 5 d, and with a tip 5 f in which thesecond part-section 5 d ends. The advance element 5 is rigidly connectedto the runner or rotor 4. The narrowing location 5 e is not absolutelynecessary, it may be arranged in an arbitrary manner in order toinfluence the characteristic oscillation of the part-sections.

The advance element 5 running with a sharp bend has a technicalparticularity which hereinafter will be described in more detail. Thefirst part-section 5 c has a first natural resonant frequency f1. Thesecond part-section 5 d has a second natural resonant frequency f2. Thetwo part-sections 5 c, 5 d are designed and are mutually mechanicallycoupled, in a manner such that the two natural resonant frequencies f1,f2 have different values. The entire advance element 5 is excited intooscillation via the resonator 1,3, and with this oscillates at afrequency f.

FIG. 6 shows an embodiment example of a rotor 4 on whose surface aplurality of sharply bent advance elements 5 are arranged in distancedmanner. In a preferred design, the piezoelectric motor 6 represented inthe FIGS. 5 a, 5 b comprises the rotor 4 shown in FIG. 6.

FIG. 7 shows the oscillation amplitude of the advance element 5 as afunction of the exciting frequency f. The advance element 5 here forexample has a resonator frequency in the range of 100 kHz.

FIG. 8 shows the oscillation amplitude of the resonator 1,3 as afunction of the exciting frequency f, as this was used for thepiezoelectric motor 6 shown in the FIGS. 5 a and 5 b. The resonator 1,3has a natural frequency with the frequencies 100 kHz and 300 kHz by wayof example.

A comparison of FIGS. 7 and 8 shows that the piezoelectric motor 6represented in the FIGS. 5 a and 5 b is designed in a manner such thatthe resonator 1,3 as well as the advance element 5 have a resonance inthe region of 100 kHz. The subsequently described technical effect is ofparticular interest. The advance element 5 is designed in a manner suchthat below the resonant frequency of 100 kHz, as shown for example at 90kHz, essentially the first part-section 5 c has a resonance behaviourwith a correspondingly high amplitude. This resonance behaviour is shownin FIG. 5 b in that the first part-section 5 c is deflected relativelyheavily, whereas the second part-section 5 d which is excited outsideits resonant frequency only undergoes a slight deflection or shapechange. This has the consequence that the rotor 4 is rotated in theanti-clockwise direction in the rotational direction D.

The advance element 5 is furthermore designed such that above theresonant frequency of 100 kHz, for example at 110 kHz as shown,essentially the second part-section 5 c has a resonance behaviour with acorrespondingly high amplitude. This resonance behaviour is shown inFIG. 5 a in which the second part-section 5 d is deflected relativelyheavily whereas the first part-section 5 c which is excited outside itsresonance frequency only undergoes a small deflection or shape change.This has the result that the rotor 4 is rotated clockwise in therotation direction D. Thus the piezoelectric motor 6 represented in theFIGS. 5 a and 5 b, as shown in FIG. 7, rotates anti-clockwise orclockwise depending on the excitation frequency. This design of thepiezoelectric motor according to the invention thus has the advantagethat it may be driven in both rotational directions, that the rotationaldirection may be selected and that the rotational direction for examplemay also be constantly changed during operation.

FIG. 9 a shows a lateral view of a piezoelectric motor 6 designed as aninner runner, with a resonator 1,3, a stator with fastening means 1 c,with an annular piezoelectric transducer 3 a, 3 b with electrical supplyleads 8, as well as a rotor with a multitude of advance elements 5arranged distanced from one another in the circumferential direction,which may be rotated about the rotation centre 4 a.

FIG. 9 b shows a section through FIG. 9 a along the section line C-C,from which the resonator 1,3 with the stator 1 and the piezoelectrictransducer 3 a, 3 b as well as the rotor 4 with the advance element 5and a shaft 4 b arranged in the centre may be seen.

FIG. 10 a shows a lateral view of a further piezoelectric motor 6 whoseshaft 4 b in contrast to the embodiment shown in FIG. 9 a is mounted ina bearing 9.

FIG. 10 b shows a section through FIG. 10 a along the section line D-D,from which the resonator 1,3 with the stator 1 and the piezoelectrictransducer 3 a, 3 b as well as the rotor with the advance element 5 anda shaft 4 b arranged in the centre may be seen, which is mounted in thebearing 9.

FIG. 11 a shows a lateral view of a further piezoelectric motor whoseresonator 1,3 in contrast to the embodiment shown in FIG. 9 a comprisestwo stators 1 and a piezoelectric transducer 3 arranged there between.

FIG. 11 b shows a section through FIG. 11 a along the section line E-E,from which the resonator 1,3 with the two stators 1 and thepiezoelectric transducer 3 arranged therebetween as well as the rotor 4with the advance element 5 and a shaft 4 b arranged in the centre may beseen.

FIG. 12 a shows a lateral view of a piezoelectric motor 6 designed as anouter runner, with a resonator 1,3, a stator 1 which is firmly anchoredvia the fastening element 1 c, two disk-like piezoelectric transducers 3a, 3 b with electrical supply leads 8, as well as a rotor 4 with amultitude of advance elements 5 arranged distanced in thecircumferential direction, said rotor being designed as a hollow runnerand being rotatable about the rotation centre 4 a. The advance elements5 are arranged projecting inwards and lie on the circular outer surfaceof the resonator 1,3.

FIG. 12 b shows a section through FIG. 12 a along the section line F-F,from which the resonator 1,3 with the stator 1, piezoelectrictransducers 3 a, 3 b and the fastening element 1 c with electricalconduits 8 may be seen. The rotor 4 with the advance elements 5 isdesigned as an outer runner and lies on the outer surface of theresonator 1,3.

FIG. 13 a shows a lateral view of a further piezoelectric motor 6designed as an outer runner. In contrast to the embodiment representedin the FIGS. 12 a and 12 b, the stator 1 with the piezoelectrictransducers 3 a, 3 b as well as the rotor 4 are mounted in a commonbearing 9 with a shaft 4 b.

FIG. 13 b shows a section through FIG. 13 a along the section line G-G,from which the resonator 1,3 fastened on the bearing 9, with the stator1 and piezoelectric transducers 3 a, 3 b as well as the rotor 4 withadvance elements, which is mounted on the shaft 4 b are visible. Theshaft 4 b is rigidly connected to the bearing 9.

FIG. 14 a shows a lateral view of a further piezoelectric motor 6 whoserotor 4, in contrast to the embodiment shown in FIG. 9 a, is designed asa hollow runner 4.

FIG. 14 b shows a section through the motor shown in FIG. 14 a along thesection line H-H, from which the resonator 1,3 as well as the rotor 4designed as a hollow runner may be seen.

FIG. 15 a schematically show the principle of how one may design thepiezoelectric motor 6 according to the invention as a linear motor. Theelectrical connections for exciting the piezoelectric element, or withsandwich designs the piezoelectric elements, are not shown.

FIG. 15 b in a schematic representation shows a section through thelinear motor according to 15 a along the section line I-I. The runner 4is designed in a rectangular and plate-like manner. In each case onepiezoelectric transducer 3 a, 3 b is arranged on the runner 4 on bothsides, wherein the runner 4 and the transducers 3 a, 3 b form aresonator 4,3 which has a main oscillation direction H. The runner 4 isdisplaceably mounted in the stator 1 in a movement direction runningperpendicular to the main oscillation direction H, and at the top andbottom in each case has an engagement surface 1 a. The stator 1comprises a multitude of advance elements 5 which are arrangedprojecting towards the runner 4 and are arranged distanced in themovement direction B. The advance elements 5, as shown in detail in theFIGS. 5 a to 5 d are designed with shape having a sharp bend and havethe resonance behaviour represented in FIG. 7. This has the result thatthe runner 4 is moved to the left or right in the linear motor 6 shownin FIG. 15 a, depending on the excitation frequency of the resonator4,3.

In the previously represented embodiment examples, the piezoelectrictransducer 3 may be arranged on the runner 4, analogously to theembodiment examples shown in the FIGS. 15 a and 15 b.

FIG. 17 a schematically shows a preferred embodiment of the invention asa linear motor 6. The runner 4 thus comprises the advance elements 5,and the stator 1 comprises at least one piezoelectric transducer 3. Theremaining features, if not stated otherwise, are designed analogously tothose of the embodiment according to FIG. 15.

FIG. 17 b schematically shows a section through a linear motor 6according to FIG. 17 a along the section line J-J. The stator 1preferably comprises an H-shaped cross section with a first arm pair 11,11′ and with a second arm pair 12, 12′. The first arm pair 11, 11′ formsa channel in which the runner 4 may be moved. The engagement surfaces 1a are located on the inner side of the first arm pair 11, 11′ and aredistanced from a connection part 13 of the H-profile. The second armpair 12, 12′ forms a further channel in which the at least onepiezoelectric transducer 3 is arranged. Its main oscillation direction Hruns perpendicularly to the movement direction of the runner 4 or to amain extension of the stator. If several piezoelectric transducers arepresent, they are distanced from one another in this main extensiondirection. On operation of the linear motor 6 the oscillations of the atleast one transducer 3 are transmitted to the second arm pair 12, 12′and from this to the first arm pair 11, 11′ by way of a lever effect.For this, the stator has a certain flexibility which permits anoscillation of the arm pair 11, 11′, 12, 12′ with respect to theconnection part 13 of the H-profile.

FIGS. 17 c and 17 d in each case schematically show a section throughthe linear motor 6 with the view according to FIG. 17 a, but with aU-shaped cross section. One or more transducers 3 are connected to abase part 14 of the U-profile or attached on a base part on an innerside (FIG. 17 c) or outer side (FIG. 17 d) of this base part. Thetransducer or transducers 3 extend preferably in the main oscillationdirection H partly or at least approximately completely over the basepart 14. The resonator 3,4 has two stable resonant frequencies. Onexciting the piezoelement 3 at a first resonant frequency, for exampleat 20 kHz, a bending and an oscillation, above all of the base 14 of theU-profile together with the arm pairs 11, 11′ results. At a secondresonant frequency, for example at 30 kHz, the base 14 remainsrelatively flat and above all only the arm pair 11, 11′ oscillates.These two resonant frequencies are matched to the resonant frequenciesof the advance elements 5 of the runner 4 and thus effect a left-runningor right-running of the runner 4. In this embodiment form as in allothers, the excitation or resonant frequencies are preferably outsidethe range of human audibility, preferably higher than 16 kHz or 20 kHz.

An extension of the stator in the plane of the drawing and perpendicularto the main oscillation direction H preferably lies in a range between 1mm to 3 mm or 30 mm, and a width of the runner 4, thus a distance of theengagement surfaces la lies preferably in a range between 1 mm to 3 mmor 20 mm. Cross sectional areas below 1 mm² and extensions of severalcentimetres may be realised.

In a preferred embodiment of the invention, with one or both of the armpairs 11, 11′, 12, 12′ in each case one of the arms has a differentnatural frequency than the other. For example a first arm 11 of thefirst arm pair in the main oscillation direction has a thickness d₁which differs from a thickness d₂ of a second arm 11′ of the first armpair. As an alternative to this or additionally, the first arm 11 of thefirst arm pair has a lever arm 1 ₁ which is different to a lever arm 1 ₂of the second arm 11′ of the first arm pair. Amongst other things, thishas the advantage that one does not need to fulfil high demands withrespect the tolerance of the dimensions of the arms 11, 11′.

For increasing the friction value or for improving the frictionalconnection between the engagement surface 1 a and the advance element 5,the corresponding surfaces for example on the advance element 5 may beenlarged (grinding, bending or by integrally shaped extensions). Theymay have a defined surface roughness, a micro-toothing or consist of asuitable pairing of material.

FIGS. 16 a, 16 b and 16 c show a somewhat modified spatial formation ofthe piezomotor according to the invention, in each case in a plan view.For an improved understanding, the rotor, here as an outer runner, andthe stator, here as a resonator, are shown individually and bothassembled.

A piezoceramic ring 3, combined with a metal plate 10 designed accordingto FIG. 16 a is brought to oscillate by way of an alternating voltage ina manner such that a radial contraction and an extension again occur.With a suitable choice of geometry the piezoceramic ring 3 and the metalplate begin to execute a torsion oscillation to the centre+where forexample a fixation is arranged. By way of these two oscillations, theradial one of the piezo-ring and the rotative one of the torsion, whensuperimposed, a point X on the outer side of the metal plate describes acurved path to the point X′ on the dashed line 10′ on the periphery ofthe deflected metal plate and back again. The second dashed line 3′shows the deflection of the piezoelement. By way of this superimposeddeflection, any part which contacts the outer side of the ring, forexample an outer runner with advance elements, is set into motion. Theconstruction may be designed as a sandwich between two piezoceramicrings or with only one piezoceramic ring as has already been discussedseveral times in the previous figures.

An outer runner designed according to FIG. 16 b with an annularlyarranged number of advance elements 5, see also FIG. 12 a with a similarshape, is designed in a manner such that the advance elements 5 do notnecessarily, but here for example have an enlarged contact surface B tothe torsionally oscillating resonator (not to be confused with, theadvance element with various part regions with various naturalfrequencies, which practically contact the part to be driven only at thetip). With the assembly of the stator 1,3 and the outer runner 4, asshown in FIG. 16 c, one recognises the principle of this drive withsuperimposed oscillation.

Regarding operation of the motor: The piezoelectric motor 6 according tothe invention comprises a stator 1 as well as the runner, wherein thestator 1 or the runner 4 may be piezoelectrically excited into anoscillation with a main oscillation direction H, is preferably operatedin a manner such that the stator 1 comprises an engagement surfacefacing the runner 4 or the runner 4 comprises an engagement surface 1 afacing the stator 1, that the stator 1 or the runner 4 comprises anadvance element 5 which runs transversely to the main oscillationdirection H and is directed towards the engagement surface 1 a, and thatthe advance element 5 on account of the oscillation may be brought intoactive connection with the engagement surface 1 a in a manner such thatthe runner 4 is moved with respect to the stator 1.

In a further method for operating the motor, one proceeds in that theadvance element comprises a first part-section 5 c as well as a secondpart-section 5 d, that the first part-section 5 c runs at an angle tothe main oscillation direction H, that the second part-section 5 d runsat an angle to the main oscillation direction H and opposite to thefirst part-section 5 c, that the first and the second part-section 5 c,5 d have a different resonant frequency, and that the runner 4 is movedin the one direction or in the direction opposite to this with respectto the stator 1, depending on the frequency of the engaging oscillationof the runner 4.

The embodiment forms presented here may be divided roughly into twogroups according to which part is designed as a resonator. With the onegroup the part on which the advance element or elements is/are arrangedis formed as a resonator so that the resonator is supported in aspring-mounted manner via the advance elements, and the advance elementsact on the other part in a driving manner via the contact locations.With the other group the part which lies opposite the advance elementsis formed as a resonator so that the movement of the resonator acts in adriving manner via the contact locations.

The piezoelectric motor according to the invention on account of itssuitable properties may for example be used for devices concerningmeasurement technology, optical apparatus, measuring instruments ortachometers etc.

1. A piezoelectric motor (6) comprising a stator (1) and a runner (4)which form a gap (7), as well as comprising a piezoelectric transducer(3) which is connected to the stator (1) or the runner (4) and whichwith the stator (1) or the runner (4) forms a resonator (1,3;4,3),wherein the resonator (1,3; 4,3) may be excited in a main oscillationdirection (H), characterised in that the stator (1) comprises anengagement surface (1 a) facing the runner (4), or the runner (4) anengagement surface which faces the stator (1), and that the stator (1)or the runner (4) comprises an elastic advance element (5) which bridgesthe gap (7) between the stator (1) and the runner (4) in a manner suchthat the advance element (5) at least temporarily lies on the engagementsurface (1 a) and said advance element (5) comprises a firstpart-section (5 c) as well as a second part-section (5 d), wherein thepart-sections (5 c, 5 d) have a different resonant frequency.
 2. Apiezoelectric motor according to claim 1, characterised in that this isdesigned as a linear motor, that the resonator (1,3;4,3) has a movementdirection (B) which runs perpendicularly to the main oscillationdirection (H), and that the engagement surface (1 a) runs in themovement direction (B).
 3. A piezoelectric motor according to claim 1,characterised in that this is designed as a rotation motor, with acircular runner (4) formed as a rotor, wherein the main oscillationdirection (H) of the resonator (1,3; 4,3) is directed radially to therotation centre of the runner (4), and the engagement surface (1 a) runsin a circular manner.
 4. A piezoelectric motor according to claim 3,characterised in that the stator (1) is designed in an annular manner,the piezoelectric transducer (3) is rigidly connected to the stator (1),and the main oscillation direction (H) runs radially to the centre ofcurvature of the stator (1).
 5. A piezoelectric motor according to oneof the preceding claims, characterised in that the advance element (5)is designed running in a straight line.
 6. A piezoelectric motoraccording to one of the preceding claims, characterised in that theadvance element (5) is part of the stator (1) or of the runner (4).
 7. Apiezoelectric motor according to one of the preceding claims,characterised in that the advance element (5) comprises an inclinationangle (α) with respect to the main oscillation direction (H), which isbetween 45 degrees and more than 0 degrees.
 8. A piezoelectric motoraccording to one of the preceding claims, characterised in that amultitude of advance elements (5) are arranged successively one afteranother on the stator (1) or runner (4).
 9. A piezoelectric motoraccording to one of the preceding claims, characterised in that thefirst part-section (5 c) and the second part-section (5 d) meet at asharp-bend location, and that the first part-section (5 c) runs at anangle to the main oscillation direction (H) and that the secondpart-section (5 d) runs opposite to the first part-section (5 c) at anangle to the main oscillation direction (H).
 10. A piezoelectric motoraccording to claim 9, characterised in that the first part-section (5 c)as well as the second part-section (5 d) are designed in a manner suchthat they have a different resonant frequency.
 11. A piezoelectric motoraccording to of the preceding claims, characterised in that theresonator (1,3; 4,3) is designed in a manner such that the stator (1) orrunner (4) is arranged in the middle and on each side of the same onepiezoelectric transducer (3) each is arranged.
 12. A piezoelectric motoraccording to one of claims 1 to 10, characterised in that the resonator(1,3; 4,3) is designed in a manner such that the piezoelectrictransducer (3) is arranged in the middle and on both sides in each casea stator (1) or a runner (4) is arranged.
 13. A piezoelectric motoraccording to one of preceding claims, characterised in that the runner(4) is designed as an outer runner.
 14. A piezoelectric motor accordingto one of the preceding claims, characterised in that the runner ismounted at a bearing location (9).
 15. A piezoelectric motor accordingto claim 2, characterised in that the stator (2) is designed running ina linear manner, that the resonator (1,3;4,3) is formed plate-like, andthat the resonator (1,3;4,3) is mounted in a linearly movable mannerwith respect to the stator (1).
 16. A piezoelectric motor according toclaim 2, characterised in that the piezoelectric transducer (3) with thestator (1) forms the resonator (1,3).
 17. A piezoelectric motoraccording to claim 16, characterised in that the runner (4) is mountedin a linearly movable manner with respect to the stator (1) andcomprises at least one advance element (5).
 18. A piezoelectric motoraccording to claim 16 or 17, characterised in that the stator (1) has anH-shaped cross section which forms two channels, wherein the runner (4)is mounted in a linearly movable manner in a first channel, and one ormore piezoelectric transducers (3) are arranged in a second channel. 19.A piezoelectric motor according to claim 16 or 17, characterised in thatthe stator (1) has a U-shaped cross section which forms a channel,wherein the runner (4) is mounted in this channel in a linearly movablemanner, and one or more piezoelectric transducers (3) are attached on abase part (14) of the U-profile.
 20. A method for driving apiezoelectric motor (6) comprising a stator (1) as well as a runner (4),wherein the stator (1) or the runner (4) is excited piezoelectricallyinto an oscillation with a main oscillation direction (H), characterisedin that the stator (1) comprises an engagement surface (1 a) which facesthe runner (4), or the runner (4) an engagement surface which faces thestator (1), that the stator (1) or the runner (4) comprises an advanceelement (5) directed towards the engagement surface (1 a), that theadvance element (5) comprises a first part-section (5 c) as well as asecond part-section (5 d), that the first part-section (5 c) runs at anangle to the main oscillation direction (H), that the secondpart-section (5 d) runs at an angle to the main oscillation direction(H) and opposite to the first part-section (5 c), that the first and thesecond part-section (5 c, 5 d) have a different resonant frequency, thatthe advance element (5) on account of the oscillation is brought intoactive connection with the engagement surface (1 a) in a manner suchthat the runner (4) is moved with respect to the stator (1), and thatthe runner (4) with respect to the stator (1) is moved in the onedirection or in the direction opposite to this depending of thefrequency of the engaging oscillation.
 21. The use of a piezoelectricmotor according to one of the claims 1 to 19 fortime-measurement-technology devices, photographic apparatus, measurementinstruments or tachometers.